So, I guess having an ear-mounted headlight has the advantange of easy access to the grub screw. Once you can access it, take a close look to make sure there is still a good slot in the screw. Find a screwdriver that is a near-perfect fit. If you don't have one, grind an old one to a nice tight fit. Be careful with the heat of grinding to avoid losing all hardness. Don't bother trying to loosen the grub screw before an overnight soaking with Liquid Wrench or your local equivalent. If it then does no let loose, you will need to do surgery. It's hard to say if the typical tapered extractor will work, but it is a big problem if it breaks off in the effort. A friend of mine just introducd me to left-handed drill bits that you use as extractors by increasing in size until there is not enough left of the screw to maintain its grip.
After the grub screw is out, I think you could drive out the lock from the bottom when the lock is turned away from the pin receptor. Otherwise, assuming you've decided the lock is shot, you could use a screw-type dent puller.
Well, that's enough of my opion. Let us know what happens.
Richard L.